1. Field of the Invention
The present invention relates to semiconductor memories that have volatile memory cells each having a capacitor and that have interfaces as of SRAMs.
2. Description of the Related Art
Recently, mobile devices such as cellular phones and the like have advanced service functions, and handling data amount therein has been increasing. Accordingly, there is a growing demand for large capacities of the work memories incorporated in such mobile devices.
Conventionally, SRAMs having simple system structure are used as the work memories of such mobile devices. However, the SRAMs are disadvantageous in terms of providing large capacities because they require more elements to constitute each one-bit cell than DRAMs. For this reason, semiconductor memories called pseudo SRAMs have been developed, which have both large capacities as of DRAMs and high usability as of SRAMs.
It is expected that mobile devices have further advanced service functions, with development of third-generation cellular phones or mobile terminals. Along with the advancement of mobile devices' functions, it is demanded that the work memories incorporated in such mobile devices have higher speed performances as well as larger capacities.
The conventional pseudo SRAMs have a function, called page mode, to execute a read operation by successively supplying column addresses. The read operation in the page mode is executed by successively supplying column addresses. In general, addresses require large numbers of bits and are supplied not only to the memories but also to other chips in the systems, so that skew is likely to be large. Therefore, the shorter the access cycle is, the greater the ratio of the address skew to the access cycle is likely to be. The greater the address skew becomes, the longer the setup and hold times of the addresses relative to timing signals have to be set. Thus, there exists a problem that the address skew is a hindrance to the shortening of the access cycle and that the data transfer rate therefore cannot be improved.